Almquist et al., "Synthesis and Biological Activity of a Ketomethylene Analogue of a Tripeptide Inhibitor of Angiotensin Converting Enzyme",J. Med. Chem., 1980, 23, 1392-1398, discloses the ketomethylene compound the formula ##STR2## This and related compounds are also disclosed by Almquist et al. in U.S. Pat. No. 4,329,473.
Natarajan et al. in U.S. Pat. No. 4,621,092 disclose compounds of the formula ##STR3## These compounds are useful as hypotensive agents due to their angiotensin converting enzyme inhibition activity and depending upon the definition of X may also be useful as analgesics due to their enkephalinase inhibition activity.
Godfrey, Jr. et al. in U.S. Pat. No. 4,604,402 disclose compounds of the formula ##STR4## These compounds are useful as hypotensive agents due to their angiotensin converting enzyme inhibition activity and depending upon the definition of X may also be useful as analgesics due to their enkephalinase inhibition activity.